Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The Nature of Energy Chapter 5 What is Energy? • When wind moves a leaf, or even a house, it causes a change. • In this case, the change in the position of the object. • Recall that work is done when a force moves an object through a distance. • The ability to do work or cause change is called energy. Energy Transfer • When an object or organism does work on another object, some its energy is transferred to that object. • You can think of work, then, as the transfer of energy. • When energy is transferred, the object upon which the work is done gains energy. • Energy is measured in joules - the same units as work. Kinetic Energy • There are two general kinds of energy. • The two kinds of energy are kinetic energy and potential energy. • Whether energy is kinetic or potential depends on if the object is moving or not. • A moving object can collide with another object and move it some distance. • In that way, the moving object does work. For example, a bowling ball knocks over a bowling pin. • Because the moving object can do work, it must have energy. • The energy of motion is called kinetic energy, coming from the Greek word kinetos meaning moving. Mass and Velocity • The kinetic energy of an object depends on both its mass and its velocity. • Think about rolling a golf ball and bowling ball at the same velocity. Which ball will roll more forcefully? • You would have to exert a greater force on the bowling ball because it has more mass than the golf ball. • Since energy is transferred during work, the more work you do, the more energy you give to the ball. • So the bowling ball has more kinetic energy than the golf ball traveling at the same velocity. • Kinetic energy increases as mass increases. • What would you do to make the bowling ball move faster? You would throw it harder, or use more force. • Therefore, kinetic energy increases when velocity increases. Calculating Kinetic Energy • Kinetic energy depends on both mass and velocity. • The mathematical relationship between kinetic energy, mass, and 2 velocity is • Kinetic energy = mass x velocity 2 Changes in Velocity and Mass • Do changes in velocity and mass have the same effect on kinetic energy? • No, changing the velocity of an object will have a greater effect on its kinetic energy than changing its mass. • This is because velocity is squared in the energy equation. • For instance, doubling the mass of an object will double its kinetic energy, but doubling its velocity will quadruple its kinetic energy. Potential Energy • Sometimes when you transfer energy to an object, you change its position or shape. • Unlike kinetic energy, which is the energy of motion, potential energy is stored. • Energy that is stored and held in readiness is called potential energy. • This type of energy has the potential to do work. Elastic Potential Energy • An archer gives potential energy to a bow by pulling it back. • The stored energy can send an arrow whistling to its target. • The potential energy associated with objects that can be stretched or compressed is called elastic potential energy. Gravitational Potential Energy • You give a different type of potential energy to an object that you can lift. • Potential energy that depends on height is called gravitational potential energy. • The gravitation potential energy an object has is equal to the work done to lift it. • Remember Work = Force x Distance • The force is the force you use to lift the object, or its weight. • The distance is the distance the object moves or its height. Therefore: • Gravitational potential energy = weight x height Different Forms of Energy • Kinetic Energy and Potential Energy have a variety of different forms. • Some of the major forms of energy are: • Mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy, and nuclear energy. Mechanical Energy • Mechanical energy is the energy associated with the motion and position of an object. • Mechanical energy can occur as kinetic or potential energy. • Examples - the school bus you ride in, a frog leaping through the air. Thermal Energy • All matter is made up of small particles, called atoms and molecules. • These particles have both potential energy and kinetic energy due to their arrangement and motion. • Thermal energy is the total energy of the particles in a substance or material. • When the thermal energy of an object increases, its particles move faster, making the temperature of the object rise. • Example - ice cream melts when its thermal energy increases. Chemical Energy • Chemical compounds such as chocolate, wood, and wax, store chemical energy. • Chemical energy is potential energy stored in chemical bonds that hold chemical compounds together. • Chemical energy is stored in foods you eat and in a match that is used to light a candle. • Chemical energy is even stored in the cells of your body. Electrical Energy • When you receive a shock from a metal door knob, you experience electrical energy. • Moving electric charges produce electricity, and the energy they carry is called electrical energy. • You rely on electrical energy from batteries or power lines to run electrical devices such as radios, lights and computers. Electromagnetic Energy • The light that you see each day is a form of electromagnetic energy. • Electromagnetic energy travels in waves. • These waves have some electrical properties and some magnetic properties. • In addition to visible light, ultraviolet radiation, microwaves, and infrared radiation are examples of electromagnetic energy. Nuclear Energy • Nuclear Energy is potential energy stored in the nucleus of an atom and is released during nuclear reactions. • One kind of nuclear reaction occurs when a nucleus splits (nuclear fission). • Another kind occurs when nuclei fuse, or join together (nuclear fusion). • These reactions release tremendous amounts of energy. • Nuclear power plants use fission reactions to produce electricity. • Nuclear fusion occurs in the sun and other stars.